This research proposal is concerned with the investigation of the macrophages' response to immobilized immune ligands, and the morphology and biochemistry of the surface adherent plasma membrane. Mononuclear phagocytes are cultured on dish surfaces coated with antigen-antibody, or with antigen-antibody and complement resulting in the loss of the functions of Fc and C3 receptors on the nonadherent membrane surface most likely by capping to the substrate-adherent membrane. The requirements for Fc receptor modulation are analyzed using inhibitors of the generation of cellular energy, pinocytosis, protein synthesis, and cytoskeletal function. Further experiments study the effects of temperature as a function of time on the speed of removal of receptor sites from the nonadherent surface. These functional studies are supplemented on the ultrastructural level, and the molecular level through the use of a monoclonal anti-Fc receptor antibody. Radioactivity labeled anti-Fc receptor antibody indicates the removal of the receptor-antigen from the nonadherent cell surface. This antibody is further used to establish precise time kinetics for receptor movement, and to measure mobility within the plane of the plasma membrane. In an additional experimental series we describe a method for isolation and analysis morphologically and biochemically of the adherent plasma membrane. This method is applied to study the effects of specific receptor modulation by immobilized (immune) ligands on the composition of the adherent segment of the cells' plasma membrane. The availability of the cytoplasmic side of this membrane also allows us to analyze by morphological means the relationship between cytoskeleton and adherent plasma membrane under the various modulating conditions.